A. Field of the Invention
The present invention relates to a method and structure for coupling a step motor shaft, especially to a method and structure which can instantly increase the initial speed of the step motor for driving the load by traveling through a predetermined back-lash distance defined between the key of the shaft coupling device and the step motor shaft.
B. Description of the Prior Art
According to conventional technology, the structure of a step motor for driving a load via a shaft coupling device is illustrated in FIG. 1. The shaft coupling device 11 is connected to a load (not shown) and mounted with a key 12 for connecting to the step motor shaft 13. Since the step motor shaft 13 is secured to the shaft coupling device 11, so the load will be driven by the step motor shaft 13 when the step motor shaft 13 rotates. Due to the resistance of the load, the initial speed for driving the load will be slow down and cannot instantly drive the load at a desired speed.
To increase the initial speed for driving the load, a conventional approach applies a clutch for progressively increasing the resistance of the load put onto the step motor. Another conventional approach uses an electronic speed controller for controlling the initial speed for driving the load in response to the moment of torsion. When the speed of the step motor is low, its moment of torsion is increased. In contrast, when the speed of the step motor is high, its moment of torsion is decreased. Accordingly, the initial speed for driving the load can be controlled by an electronic speed controller to be progressively increased. Eventually, the step motor can drive the load at a desired speed.
However, the mechanism for controlling the step motor by a clutch is complicated, which will inevitably increase the manufacturing cost. On the other hand, if the initial speed for driving the load is controlled by an electronic speed controller, the time and distance required for acceleration will be too long. Thus, for a step motor of low power, it would be desirable to improve its initial speed for driving a load using a simple mechanism.